Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Jonathan C. Barnes, Albert C. Fahrenbach, Scott M. Dyar, Marco Frasconi, Marc A. Giesener, Zhixue Zhu, Zhichang Liu, Karel J. Hartlieb, Ranaan Carmieli, Michael R. Wasielewski, J. Fraser Stoddart

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Abstract

The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylenebridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquatp-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ring encircles the DNP unit. Reduction of the CBPQT 4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY •+ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+)ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET =1.33 × 107 s-1) and activation energy (ΔG = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus-Hush theory.

Original languageEnglish
Pages (from-to)11546-11551
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number29
DOIs
Publication statusPublished - Jul 17 2012

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Barnes, J. C., Fahrenbach, A. C., Dyar, S. M., Frasconi, M., Giesener, M. A., Zhu, Z., Liu, Z., Hartlieb, K. J., Carmieli, R., Wasielewski, M. R., & Stoddart, J. F. (2012). Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle. Proceedings of the National Academy of Sciences of the United States of America, 109(29), 11546-11551. https://doi.org/10.1073/pnas.1201561109